1. Field of the Invention
The present invention relates to magnetic recording apparatus, and more particularly to an improved bias control arrangement.
2. Description of the Prior Art
In the direct recording of signals on magnetic tape, it is usually required that the intelligence signals to be recorded be superimposed upon a high frequency bias signal. That bias signal, for obvious reasons, is selected to be of a frequency which is three to five times higher than the highest frequency anticipated in the intelligence signal. With intelligence or data signals having a frequency of up to 4 MHz, the bias signal must be from 12 to 20 MHz. In providing circuitry for accommodating the wide band-width for the recording of the data signals with low distortions thereof and, at the same time, effect a transfer of substantial power from the bias signal has, heretofore, entailed relatively complex circuitry. An example of such a circuit is shown in U.S. Pat. No. 3,381,098. In that patent, there is provided separate amplification channels for the bias and data signals as well as separate coupling transformers.
Because of the coupling problems and the relatively low efficiency thereof, it has been necessary to provide a relatively large amount of power in the head driving bias amplifier. That means, since the coupling to the head is inefficient, that the driving amplifier must be capable of dissipating much of the power developed by that amplifier.
Additionally, when one source of high frequency bias is used to drive a plurality of recording heads, care must be taken to avoid the introduction of cross-talk between heads by reflection back through the bias channels. To this end, bias traps or filters are used; but such traps are limited in scope.